We plan to investigate the structure of NRI-phosphate, the transcription activator of nitrogen regulated genes in Escherichia coli and the mechanisms of the interconversion of NRI and NRI- phosphate by NRII and PII. We also plan to investigate at the molecular level the activation of transciption of GLN1, the structural gene for glutamine synthetase in Saccharomyces cerevisiae in response to the availability of glutamine and glutamate. We have shown that this activation depends on the product of GLN3 and appears to be antagonized by the product of URE2. We plan to clone these genes to identify their products and to investigate the putative effect of the URE2 product on GLN3 or its product and the putative interaction of the GLN3 product with the GLN1 promoter. We plan to investigate whether products of additional genes play a role in this regulation. We shall also investigate the role of the GLN3 and URE2 products in the regulation of other genes, such as the structural genes for the NAD-linked glutamate dehydrogenase and amino acid permeases. We plan to elucidate the mechanism responsible for the activation of GLN1 expression in response to purine deprivation and of the mechanism responsible for the activation of expression of the genes for amino acid and permeases, GAP1 and PUT4, in response to nitrogen deprivation.